1. Field of the Invention
The present invention relates to a portable wireless terminal. More particularly, the present relates to a wireless communication interface for a portable wireless terminal, which wirelessly communicates with other devices via a free space.
2. Description of the Related Art
In the field of a portable wireless terminals used for communications, such as a cellular phone or a personal digital assistant (PDA), and in the field of hand-held electronics such as a digital camera or an mp3 player, research has already been performed on a peripheral interface which provides communication between devices by mounting an IR-based module. The IR-based module is typically an infrared data association (IrDA) module, and related products have been developed and commercially used. In contrast to radio frequency (RF) communication protocols such as Bluetooth or Zigbee, infrared communication has advantages including there are no cross talk problems between devices, as well as providing reliable security, and a low-power usage design.
FIG. 1 illustrates an infrared communication system according to the prior art. The infrared communication system 100 includes first and second portable wireless terminals 110, 120. Each of the portable wireless terminals 110, 120 includes a light emitting diode (LED) for transmitting an infrared signal, and a photodiode (PD) for receiving an infrared signal. Communication between the first and the second portable wireless terminals 110, 120 is possible only when the two terminals are aligned. In another words, unlike, for example, line of sight, a radio link in IR is secured only when the two terminals 110, 120 aligned within the divergence range of each other's transmissions.
Moreover, as infrared rays are invisible, each of the portable wireless terminals 110, 120 transmits an infrared signal having a divergence angle greater than 30°, so as to easily secure the radio link. Referring to FIG. 1, the first portable wireless terminal 110 transmits an infrared signal 130 having a divergence angle θ1 greater than 30° to the second portable wireless terminal 120. An intensity distribution 140 of the infrared signal 130 on a plane perpendicular to a traveling direction of the infrared signal 130 shows the Gaussian (bell) form which is intense at the center, and weak at both ends.
Thus, the more closely the terminals 110, 120 are aligned with each other, the greater the likelihood that terminal 120 receives the most intense IR signal. In fact, the permissible distance between the terminals 110, 120 is at a maximum in the case where the alignment is such that the intensity received of the IR signal received is near or at the center of the Gaussian distribution.
However, one of the drawbacks of the aforementioned infrared communication system 100 as described is that infrared rays are not visible to the human eye, and thus there is difficulty to intuitively check communication security, and to secure a radio link. Also, due to the large divergence angle of an infrared signal, the infrared communication system 100 has difficulties in communicating with high speed and driving with low power. Accordingly, there is a long felt need in the art to provide a system that overcomes at least some of the drawbacks of the conventional infrared communication system.